the.com/ancient rocks
the planet's diary, written in stone before anyone thought to keep a diary.
means rock formations dating back hundreds of millions to billions of years, preserving records of earth's early history in their mineral structure.
from from geology's recognition that rock layers form sequentially, so the deeper and more altered the stone, the older the story it holds; radiometric dating later gave these guesses actual numbers.
oldest confirmedacasta gneiss, roughly 4 billion years old
oldest mineralzircon crystal dated at 4.4 billion years
earth's ageonly 500 million years older than that zircon
most rock recycledplate tectonics erased almost all early crust
for instance
acasta gneiss — canada, northwest territories, about 4 billion years old
jack hills zircon — western australia, 4.4 billion year old crystal
isua greenstone belt — greenland, 3.7 to 3.8 billion years, early life clues
barberton greenstone belt — south africa, 3.5 billion years, ancient microbial traces